GODRIVER-2109 Prevent a data race between connecting and checking out a connection from the resourcePool.

[matthewdale]

GODRIVER-2109

There is currently a data race on the field connection.desc between setting it at connection.go#L231 and reading it at pool.go#L199 and pool.go#L535. The data race occurs when the resourcePool.Maintain() function adds connections to satisfy minPoolSize (only when minPoolSize > 0). The unconnected connections are added to the resourcePool and then connected in a separate goroutine, which results in concurrent access to the connection.desc field when another goroutine attempts to get the connection from the resourcePool.

Changes:

• Update resourcePool.Maintain() and pool.connectionInitFunc() to wait for a connection to finish connecting before making it available to check out from the resourcePool.
• Add a test that triggers the data race when run with the data race detector enabled.

[matthewdale]

Closing in favor of #728